A contactless switching system is implemented for example in the form of a contactlessly acting position or safety switch and is used for monitoring safety-relevant areas or generally for checking the mutual position of two parts, where at least one of the two parts can be moved independently of the other. Typical application scenarios are for example guard doors or protective covers which provide a protective circuit-breaker tripping function in a safety-relevant position.
A contactless position or safety switch consists of at least two mutually independent moving parts which are usually referred to as sensor and signal generator. The communication between sensor and signal generator takes place for example by means of magnetic or also electromagnetic alternating fields.
For example, upon receiving a request from the sensor the signal generator sends a response which contains an identification number or serial number and usually a checksum. The “Cyclic Redundancy Check” (CRC) method, inter alia, is suitable as a possible calculation rule for the checksum. This permits transmission errors to be reliably detected with a high level of probability. The position or safety switch allows access to (“releases”) the safety-relevant area only if the signal generator is located within a defined effective range relative to the sensor. A release does not take place if, due to a transmission error, the received checksum does not correspond to the calculated checksum.
At the present time position or safety switches can be operated with different types of encoding schemes. A distinction is made between group encoding, family encoding, individual encoding and master encoding.
In family and group encoding, only one family or, as the case may be, one group of sensors and signal generators match one another. In order to implement the encoding a part of the serial number is usually used for identification purposes, the number allowing a particular family to be inferred when a signal generator enters the effective range. Another possible implementation is a serial number list which is available to the sensor. Only signal generators that have a corresponding serial number trip a safety circuit on the sensor. The family encoding variant is mostly implemented on a manufacturer-dependent basis and prevents flexible use of the signal generators and sensors with products from other manufacturers. As a rule an interaction with products of other manufacturers is not desirable on safety or security grounds and consequently is deliberately avoided.
With individual encoding, one signal generator and one sensor match each other only as a pair. Other sensors or signal generators play no role in this case. The sensor recognizes one serial number only and ignores any signal generator with a different serial number.
With master encoding, a master-encoded signal generator activates both types of sensors from the same manufacturer, individual- and family-encoded. Master-encoded signal generators are intended for use by maintenance personnel during commissioning or maintenance activities. The master-encoded signal generator assumes the function of a master key.
In the present prior art the sensor of the position or safety switch detects the respective encoding type on the basis of the signal generator serial number and proceeds accordingly. In this case the detection based on specific separate or designated areas of the signal generator serial number can be crucial. However, since the serial number of the signal generator cannot be changed, the encoding type is also predefined from the outset. This means that an operation with a specific sensor is only possible in the case of quite specific serial numbers, that is to say when the serial number of the signal generator lies in the sensor's permitted serial number range. Signal generators from other manufacturers may occasionally work with sensors for which they are not intended if by chance they happen to fall into one of the specific serial number ranges.